The present invention relates to a combination of piston rings for use in an internal combustion engine, and more particularly, to the combination including at least one compression ring and at least one oil ring.
In accordance with recent requirement in higher engine performance, various machine components of the internal combustion engine are subjected to severe working conditions, and the engine must provide a prolonged durability. Piston rings are operated under higher engine rotation, higher temperature, and higher planner pressure than before, and enhancement of durability is highly required. Further, in accordance with a demand in improvement on engine performance and reduction in engine size, various combination of compression rings and oil rings are provided in an gasoline engine and Diesel engine, such as a combination of three compression rings and two oil rings, a combination of three compression rings and a single oil ring, a combination of a two compression rings and a single oil ring and a combination of a single compression ring and a single oil ring.
In order to improve durability of the piston rings, wear resistant treatment is effected on sliding surfaces of the piston rings such as a high hardness chromium plating and nitriding treatment. However, wear resistance in a conventional piston ring having the chromium plating is still insufficient. On the other hand, the nitriding treatment provides excellent wear resistance, and therefore, the nitriding treatment is becoming popular and is used for a first compression ring or a top ring which suffers from severe working condition since the top ring is positioned closest to a combustion chamber among the piston rings installed on a piston. Still however, the conventional piston ring provided with the nitriding treatment is still insufficient in wear resistance, scuffing resistance, and anti-attacking performance against an opposing component in relative sliding relation to the piston ring.
In order to overcome the above-described problems, laid open Japanese Patent Application Kokai Hei 7-239032 discloses a combination of a plurality of compression rings and at least one oil ring for use in an internal combustion engine. In the combination, an ion plating layer is formed on an outer peripheral sliding surface of a first compression ring and the at least one oil ring. By the formation of the ion plating layer, wear resistance, scuffing resistance, anti-attacking performance against an opposing component and corrosion resistance are improved in comparison with the conventional piston ring combination provided with the nitriding layer. Here, individual development of the surface layer for the compression ring and the oil ring is required in an attempt to further improve wear resistance, scuffing resistance, anti-attacking performance against the opposing component, and corrosion resistance.